Ballantine 340 User manual

90100141A
Printed in U.S.A.
MODEL
340
RF MILLIVOLTMETER
BALLANTINE LABORATORIES, INC.
P.O. BOX 97
BOONTON, NEW JERSEY 07005 USA
201·335·0900/TWX: 71 0·987-8380 JUNE 1972

WARRANTY
All Ballantine Laboratories, Inc. products are
warranted against defects
in materials and work-
manship. This warranty applies for one year from
the date
of delivery, except for vacuum tubes and
batteries, or,
in the case of certain major compo-
nents listed in the instruction manual, for the
specified period.
We will repair or replace products
which prove to be defective during the warranty
period. No other warranty is expressed
or implied.
We are not liable for consequential damages.
CERTIFICATION
The equipment supplied on your order meets all applicable published Ballantine
specifications
as determined by thorough testing and inspection. Ballantine's calibration
measurements are traceable to the National Bureau
of Standards. All instruments used
in calibrating Ballantine products are standardized by systematic reference to NBS-trace-
able standards as described in the validation procedures shown below.
REFERENCE STANDARDS
DC
10mV-750V 0.01-0.04%
20Hz-50kHz
0.5V-500V
0.03%
20Hz-10M
Hz
0.5V-100V 0.1%
DC-30MHz
0.5V-100V
0.5%
DC-700MHz
10W-0.5V 1%- NBS
10MHz-1000MHz
1V-300V 1%- NBS
_t
WORKING STANDARDS
1kHz TRANSFER VM BALLANTINE. D1094
HF TRANSFER VM BALLANTINE. MODEL 393
MICROPOTENTIOMETERS BALLANTINE 440
RATIO TRANSFORMERS. GERTSCH
CALIBRATION CONSOLE 100Hz-100kHz FOR
0.25%
ACCURACY INSTRUMENTS
LEVEL CHECK-DAILY
ATTENUATOR CHECK- 6 MONTH
~
DISTORTION CHECK- 1 MONTH
FREQUENCY RESPONSE CHECK- 3 MONTH
GROUND CURRENT CHECK- 3 MONTH
•
CALIBRATION CONSOLES 2Hz-20MHz FOR
1%-3% ACCURACY INSTRUMENTS
-
LEVEL CHECK- 1 WEEK
.._
ATTENUATOR CHECK- 6 MONTH
DISTORTION CHECK - 3 MONTH
a
FREQUENCY RESPONSE CHECK- 3 MONTH
GROUND CURRENT CHECK- 3 MONTH
lr
CROSSCHECK CONSOLE 2-20MHz FOR
~
1%-3% ACCURACY INSTRUMENTS
LEVEL CHECK- 1 WEEK
.._
ATTENUATOR CHECK- 6 MONTH
DISTORTION CHECK - 3 MONTH
FREQUENCY RESPONSE CHECK- 3 MONTH
GROUND CURRENT CHECK- 3 MONTH
Ballantine's QualityAssuranceprogram satisfied the requirements of MIL-0-9858.

1.
2.
INSTRUCTION BOOK CONTENTS
FOR
MODEL 340 RF MILLIVOLTMETER
GENERAL INFORMATION
Page
1
1.1 Features ................ .. .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. .. .. . .. .. . .. . .. .. .. . .. .. . .. .. .. .. .... .. .. .. .. .. .... .. 1
1.2 Some Applications of the Model 340 .. .. .. .. .. .... . .. . .. .. . .. .. .. .. .. . .. .. .. .. .. .. . .. .. .. . .. .. .. .. .. . 1
1.3 Technical Characteristics ....................................................................... 1
OPERATION ..................................................................................................... .. 1
1
1
2.1 Power Connection ...........
2.1.1 Line Voltage Conversion .........................................................................
2.2 Starting Procedure ........... ..
1
3
2.3
2.4
2.2.1
Warmup Period .. ..
Function of Controls
Voltage Measurements ..... ..........................................................................
2.4.1 For True RMS Voltage Measurements Below 30 mV ............................ ..
2.4.2 For True RMS Voltage Measurements Above 30 mV ..............................
3
3
3
3
2.5 Possible Error Sources .. .. .... .. .... .. .. .. .. .. . .. .. .... .. . .. .. .... . .. .... .. .. . .. .. .. .. .. .... .. .. .. .... .. .. .. .... 4
2.S.1 Indicator Remains in Extreme Left Position .. .. .... .. . .. .. .. .. . .. . .. .. . .... .. .. .. ... .. . 4
2.5.2 Indicator Remains in Extreme Right Position.......................................... 4
2.5.3 Indicator Reads High and Pointer Stays on &ale for Next Higher Range 4
2.5.4 Indicator Beats or Flutters
.... .................................................................... 4
2.5.5 Loading Errors ......................................................................................... 4
2.5.6 Voltage Drop in Connecting
Leads .......................................................... 4
2.5.7 Stray Field Pickup .................................................................................... 5
2.5.8 Transmission Line Effects ........................................................................ 5
2.5.9 Ground Current Errors ............................................................................ 5
2.5.10 Response and Waveform Errors .............................................................. 5
2.6 Use of the DB
Scale .. .. .. .. .. .. .. .. .. ... .. .. . .. .. .. .. .... .. ... .. .. ... .. .... .. .. .. .. ...... .. .. .. .... .. .... .. 6
2.7 Effect of
DC Component...................................................................................... 6
2.8 Overload Characteristics ..... 6
2.9 Effect of Power Line Voltage Variations .............................................................. 6
2.10 DC Output ............................ ................................................................................ 6
3. CIRCUIT DESCRIPTION ....... .. ............ .. ... .. ........ .. . .. . .. ............ .. .. .. .. .. .. .. . .. .. . .. .. .. . .. . .. 6
3.1 Probe .................................................................................................................... 7
3.1.1 Model 1340 Probe Attenuator ................................................................ 7
3.1.2 Model 2340 Coaxial Adapter .................................................................. 7
3.1.3 Model 4340 Probe
Tip ............................................................................ 7
3.1.4 Model 5340 Tee Adapter ........................................................................ 7
3.1.5 Model 6340 High Voltage Attenuator ...................................................... 7
3.2 Chopper Input .... .. .. . .. .. .. .. .. . .. .. .. .. .... .. .. .. .. .. .. .. .. .... . .. .. .. .. .. .. .. .. . .... .. .. . .. .. . .. .. .. .. .. . .. . .. .. 7
3.3 .. Input Amplifier .................................................................................................... 8
3.4 Midsection Attenuator .......................................................................................... 8
3.5 Output Amplifier and Signal Rectifier .............. ................................................. 8
3.6 Power Supply ........................................................................................................ 8
4. MAINTENANCE ............... .. .. .. .... .. .... .. ......... .. . .. . .. ..... .. .. .... .. .. . .. .. .. .. .. .. . .... .. .. . .. . .. .. . 8
4.1 .General ........ ..................... .............. .................................................................... 8
4.2 Recommended Maintenance ....
8
. I .

5.
6.
7.
4.3 Necessary Maintenance Equipment .
4.3.1 Stable Signal Source
4.3.2 Sensitive AC Vacuum Tube Voltmeter
4.3.3 Sensitive
DC Vacuum Tube Voltmeter .
4.3.4 Tube Checker .
4.4 Removal of the Case .
4.5 2,000 Hour Check .
4.5.1 Scale Adjustment .
4.5.2 Sensitivity Adjustment
4.5.3 Noise Check .
4.5.4 Range Switching Check
4.5.5 DC Output Check
4.5.6 Stability with Line Voltage .
4.6 4,000 Hour Check
4.6.1 Chopper Supply Adjustment
SERVICING AND TROUBLESHOOTING
5.1 Necessary Equipment .
5.2
5.3
5.4
5.5
5.6
5.7
5 .1.1 Stable Signal Source
5.1.2 Sensitive AC Vacuum Tube Voltmeter .
5.1.3 Sensitive DC Vacuum Tube Voltmeter
5.1.4 Tube Checker .
Simple Service Problems .
5.2.1 Removal of the Instrument Case .
5.2.2 Pilot Light Replacement .
5.2.3 Fuse Replacement
5.2.4 Line Voltage Conversion .
General Instructions
Signal Tracing .
Chopper Replacement
Probe Replacement
Troubleshooting Chart .
SHIPPING INSTRUCTIONS .
REPLACEMENT PARTS LIST
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
ILLUSTRATIONS AND DIAGRAMS
Ballantine Model 340 RF Millivoltmeter with Adapters
Rack Panel Mounted Ballantine Model 340-S/2 RF Millivoltmeter
..
Model 340 Location of Controls .
Model 340 Input Impedance
Model 340 Transmission Line Errors
Model 5
340 VSWR .
Figure 7 Model 340 Simplified Schematic . . ...............
Figure 8 Model 340- Right Hand Side View . ....................
Figure 9 Model 340- Left Hand Side View, Input Shield Removed .
8
8
8
8
8
8
8
8
9
9
9
9
9
10
10
10
10
10
10
10
10
10
10
10
10
10
10
11
11
11
11
13
16
III
III
2
4
5
5
6
14
15
Figure 10 Model 340 Wiring Diagram . .. ...................... .. .. .... .. .... .. ... Rear
TABLES
TABLE I DB Level Conversion 6
- II -
Page

Model 1340
Model 2340
Model 5340
Model 4340
Figure 1. Ballantine Model 340 RF Millivoltmeter with Adapters
Figure 2. Rack Panel Mounted Ballantine Model 340-S/2 RF Millivoltmeter
- III -

1. GENERAL INFORMATION
1.1 Features Frequency Range 0.1 Me to > 1000 Me
The Ballantine Model 340 RF Millivoltmeter is a sensitive,
wideband, rms-responding voltmeter with a voltage range
from 300
p. V to 3 V, frequency range of 100 kc to 700 Me,
logarithmic indicator and a basic accuracy of better than
4%.
It brings to high frequency voltage measurements the same
convenience of logarithmic scales, sensitivity and accuracy
that has always been associated with Ballantine voltmeters.
A feature of the Ballantine Model 340
RF Millivoltmeter is
its rms response to distorted sinewave voltages. This is
particularly important at high frequencies because all exist-
ing calibration standards are based on rms-responding de-
vices. High frequency waveforms are often highly distorted
and the means for measuring this distortion are limited.
Signal voltages are measured
in the Model 340 by a probe
which is connected to the voltmeter
by 3 feet of cable. This
allows positioning the probe exactly at the
point at which
the voltage measurement
is desired, thus minimizing errors
due to transmission effects.
The basic
input to the probe is coaxial - a flexible Ys inch
diameter bellows is the center conductor and the outer con-
ductor is a Ys-24 external thread. For input voltages above
30 mV, a probe attenuator (Model 1340) is first connected
to the probe. This probe attenuator has the same flexible
center conductor and threaded outer conductor
as the probe
itself. Customer-designed adapters can be used to make con-
nections to either the probe or the probe attenuator and
probe when the very shortest transmission paths are re-
quired. For less demanding applications the Model 340 is
supplied with a complete set of
input adapters. A coaxial
adapter (Model
2340) allows the probe to be connected to
female Type N and
BNC connectors. A spring-loaded probe
tip (Model
4340) is supplied for in-circuit measurements,
and a Tee-adapter (Model 5340)
is available to match the
probe to a
50 ohm transmission line.
1.2 Some Applications of the Model 340
RMS voltage measurement in grounded circuits
High frequency transistor measurements
Voltage measurements on coaxial systems
High frequency bridge measurements
1.3 Technical Characteristics
Voltage Range 300 p. V to 3 V in 8 ranges of 10 db each
Response
Accuracy
Allowable Max
Crest Factor
Scales
Probe Input
Impedance
Mean Square
DC Output
Input Power
Accessories,
Supplied
Accessories,
Optional
Vacuum Tubes
and
Semiconductors
Dimensions
(inches)
Weight (pounds)
calibrated to 700 Me
True rms, all voltages
Specified in % of reading
at any
point on the scale
0.1 -100 Me ±4%
100 -700 Me ± 10%
300
p.V - 1 mV
1 mV - 3 mV
3 mV -10 mV
10 mV -30 mV
30 mV -100 mV
0.1 v - 0.3 v
0.3 v - 1.0 v
1.0 v - 3.0 v
200 -60
60 -20
20 -6
6 - 2
200 -60
60 -20
20 -6
6 - 2
Two logarithmic voltage scales,
0.95 to 3.3 and 3.0 to 10.6
One linear decibel scale, 0-10
300
p.V -30 mV
30 mV - 3 V >25 kQ and 4 pF
> 1MQand4pF
0.1 to 1.0 V repeated for each 10 db
ac range. 20 kQ source impedance
115/230 V, 50-420 cps, 40 W
Probe Attenuator, Model 1340
Coaxial Adapter,
Model2340
Probe Tip, Model 4340
Tee Adapter, Model 5340
High Voltage Attenuator, Model 6340
2-12AX7, 2-6AU6A, 1-6X4,
1-0A2, 1-0B2WA, 2-2NS25,
2 -S282G, 4-1N816, 5 -1N1692,
2 Probe diodes (BL Special)
Portable:
13 H, 7Y2 W, 9Y2 D
Rack:
SY2 H, 19 W, 8Y2 D
Portable or Rack, 16
Shipping weight: Portable 22, rack 34
2. OPERATION
2.1 Power Connection
The voltmeter is supplied ready to operate on 105 -125 V,
50 cps -420 cps or
210- 250 V, 50 cps -420 cps power line,
as indicated on the decal mounted adjacent to the power cord.
2.1.1 Line Voltage Conversion from 115 V to 230 V
or vice versa is possible. For conversion from 115 V
operation to 230 V operation, connect the power trans-
former leads as follows:
Disconnect black-red lead from terminal 1 and
black-yellow lead from terminal
3, and connect
- 1 •
both together to terminal 2. Replace fuse Fl 0.4
ampere by 0.2 ampere Slo-Blo fuse. Detailed in-
formation for 115 V /230 V conversion is given
on the schematic at the end of this instruction book.
2.2 Starting Procedure
Insert the three-prong plug into a proper ac power outlet.
Use conversion unit where only two-prong outlets are avail-
able. Turn the function switch from OFF position. The pilot
light should glow.
The instrument is ready for use after a
short warmup period.

ADJUSTMENT
PILOT LIGHT
FUSE
Figure 3. Model 340- Location of Controls
- 2 -

2.2.1 Warmup Period
The instrument is usable after approximately 20 sec-
onds. After 15 minutes the indication will be within
1.0% of the final value.
When the instrument has no~ been in use for many
months or has been stored in high humidity allow a
warmup period of at least one hour.
NO SOURCE OF HEAT SHOULD BE CLOSE TO THE
BACK OF THE INSTRUMENT. PERMIT AIR TO CIRCU-
LATE FREELY AROUND THE VOLTMETER TO AVOID
EXCESSIVE TEMPERATURE RISE IN THE INSTRUMENT.
The voltmeter is calibrated in the vertical position. For con-
venience in reading, a tilting device is provided beneath
the case.
2.3 Function of Controls (see fig 3. for control locations)
Function Switch
OFF Turns instrument off.
STANDBY Turns instrument on with the exception
of the chopper. Use this switch position
between series of measurements to pro-
long life of chopper.
METER Turns chopper on and allows instrument
to be used
as a calibrated voltmeter.
NULL Biases meter on-scale with no signal in-
put. Use to set NULL adjustment and for
sensing voltages below the normal mini-
mum reading of 300 microvolts.
Range Selector
FULL
SCALE Selects voltage range of instrument
in 10
db steps. Voltages from 300 tL V to 30 mV
are measured without probe attenuator.
Voltages from 30 mV to 3 V must be
measured with probe attenuator
in place
as well as with correct position of FULL
SCALE range selector.
Panel Adjustments
NULL
SENS
SCALE
With shielded, open-circuit input on 1m V
range, and function switch at NULL,
rotate NULL adjustment control for min-
imum i-ndication. This adjustment should
be made after a
15 minute warmup each
time the instrument is turned on and be-
fore the start of any critical measurements.
Allows a small adjustment
in voltmeter
sensitivity to correct for changes due to
component aging.
Adjusts a biasing current to the indicator
so that full scale on one range will cor-
respond exactly to bottom scale on the
next higher range.
- 3 -
2.4 Voltage Measurements
2.4.1
For True RMS Voltage Measurements
Below 30 mV
Set
Function Switch
Range Selector
To
METER
30 mV
Connect the unknown voltage to the probe input using
the proper adapter
as required and rotate the range
selector counterclockwise until an indication appears
on the meter scale. Take the reading from the scale
indicated by the range selector. Because of the loga-
rithmic meter scale and Ballantine special design, the
accuracy of the measurement is the same at any
point
on the scale.
After a
15 minute warmup, and whenever a series of
critical measurements are to be made
on either the
1
mV or 3 mV range, check the NULL adjustment.
2.4.1.1 NULL Adjustment serves to "zero" or
cancel out small residual voltages in the
input
system of the voltmeter. Since these residuals
tend to be a function of time and temperature,
the adjustment should be made and checked
frequently for greatest accuracy.
To make the NULL adjustment:
Set To
Function Switch NULL
Range Selector 1 mV
Shield the probe input- for example, by con-
necting the Coaxial Adapter, Model 2340, to the
probe
but not screwing it all the way on to con-
nect the center conductors. Allow a few minutes
for any heat generated in handling the probe to
dissipate. Rotate the NULL adjustment for a
minimum indication.
The minimum indication should fall between
1 - 3 db on the meter scale. A higher null
is
an indication of excessive noise or thermal po-
tentials and should be investigated. (See para-
graph 4.5.3)
2.4.2 For True RMS Voltage Measurements
Above
30 mV
Set
Function Switch
Range Selector
Attach
Probe Attenuator, Model 1340
To
METER
3 v
To
Probe
Connect the unknown voltage to the probe attenuator
input using the proper adapter as required and rotate
the range selector counterclockwise until an indication
appears
on the meter scale. Take the reading from the
scale indicated by the range selector.
After a
15 minute warmup and whenever a series of
critical measurements are to be made
on either the
0.1 V or 0.3 V range, check the NULL adjustment (see
paragraph 2.4.1.1)

2.5 Possible Error Sources
The causes of some measuring difficulties are listed below:
2.5.1 Indicator Remains in Extreme Left Position
This condition may be caused by:
a) Power cord disconnected
b) Fuse open
c) Function switch in OFF or STANDBY
position
d) Input voltage lower than range selected
e) Failure to remove Probe Attenuator for
measurements below 30 mV
2.5.2 Indicator Remains in Extreme Right Position
This condition may be caused by:
a) Input voltage higher than range selected
b) Failure to attach Probe Attenuator for
measurements above 30 mV
c) Excessive external fields
d) Excessive ground currents
2.5.3 Indicator Reads High and Pointer Stays on
Scale for Next Higher Range
This condition may be caused by:
a) Function switch in NULL position
b) Excessive external fields
c) Excessive ground currents
2.5.4 Indicator Beats or Flutters
This condition may be caused by:
a) Large spurious input voltage at or near 94 cps
b) Strong magnetic fields such as exist adjacent to
certain power transformers and line voltage
regulators
c) Noisy or unstable input signal
Because of the wide frequency range and high sensltlvtty
of the Model 340, other measuring errors may be introduced
when proper measuring techniques are not used.
The most
common error sources are listed below. A comprehensive
analysis of errors is given in NBS Conference
on Standards
and Electronic Measurements paper "Techniques and Errors
in High Frequency Voltage Calibration," by Dr. E. Uiga
and
W. F. White. A copy of this paper is available without
charge from Ballantine Laboratories.
2.5.5 Loading Errors can occur whenever a source of
emf with other than zero source impedance is measured
by a voltmeter with other than infinite
input imped-
ance. Current drawn by the voltmeter produces a volt-
age drop in the source impedance and the resulting
measured terminal voltage differs from the emf by the
amount
of this voltage drop.
The Model 340 is a high input impedance device. For
input voltages below 30 m V, the low frequency input
impedance can be represented
as more than 25,000
- 4 -
ohms in parallel with 4 pF. Above 30 mV the shunt
resistance can be considered infinite while the capaci-
tance remains approximately at 4 pF. However, at high
frequencies this situation changes. Both the resistive
and capacitive components
of input impedance are
frequency sensitive -shunt resistance decreases with
frequency, shunt capacitance increases. This is shown
in figure
4.
50k
30
20
IOk
7
3
2
I k
0.7
0.5
0.3
0.2
0.1
' '
--
I I ',
~T RESISTANCE
'
'
IOpF
7
......_
h \
INPUT CAPACITANCE \
5------
--""'r-------'r'"- ------ --- -
_,
3 \
2 I I
"'
'
-INPUT < 30mV '\. I
---INPUT > 30mV
'
0.1 0.5 5 I0
50 100 200 400 700
FREQUENCY IN Me
Fig. 4. Model 340 Input Impedance
For any critical voltage measurement it is necessary to
check for loading errors by determining the actual
source impedance
of the emf at the frequency of inter-
est and, with the aid of figure 4, the input impedance
of the Model 340. The relationship between source
emf, Es, terminal voltage,
Vr, source impedance, Zs,
and voltmeter impedance, Zr, is given by:
Zs
Es = Vr (1 + Zr )
2.5.6 Voltage Drop in Connecting Leads can cause
appreciable errors at high frequencies when the induc-
tive reactance of these leads becomes large and the
input impedance of the voltmeter has decreased from
its low frequency value.
The situation is similar to the
loading error effects discussed in 2.5.5.
In this case
the impedance of the connecting leads
is analogous to
the source impedance.
Coaxial connections
i:o the Model 340 should be made
whenever possible to reduce the error due to voltage
drop in connecting leads. The Model 2340 Coaxial
Adapter, supplied with the Model 340, converts the
probe
input to accept female type N or BNC connect-
ors. It can be used, as can all the adapters, both with
and without the probe attenuator for measurements
over the entire voltage range.
The Model 4340 Probe Tip with its associated ground
lead should not be used at higher frequencies if errors
due to the voltage drop in connecting leads is suspected.
The inductance of the ground lead is approximately
0.1 1-'H which at 100 Me represents a reactance of
63 ohms.

2.5.7 Stray Field Pickup is particularly troublesome
at high frequencies. Any loop in the signal input cir-
cuit can have a voltage induced in it that is proportional
to the area of the loop, the stray field density, and
the frequency.
Again, coaxial connections are the best when stray field
pickup
is suspected. Location and removal of the of-
fending sources should be tried, and every attempt
made to reduce the loop area at the signal input.
2.5.8 Transmission Line Effects have to be consid-
ered whenever the distance between the voltage to be
measured and the Model 340 probe input
is not negli-
gibly short compared to a wavelength. The Model 340
is a high impedance device and will therefore introduce
reflections on any transmission line. These reflections
produce a voltage standing wave pattern. The magni-
tude of the voltage standing wave radio determines the
maximum difference that can exist between the source
of voltage to be measured and that indicated by the
Model 340. The actual difference will depend
on the
distance between the source and the Model 340.
Figure 5 shows the error that will exist when the
Model 340
is connected to the voltage source by a
short section of 50 ohm coaxial transmission line. This
set of curves
is derived from transmission line equations
and the input capacitance of the Model 340 (see figure
4).
%ERROR
§::§. XIOO
Es
30
LENGTH (L) IOcm 5 3 3
_I I I I~'""""
i/
:I , I
OF PROBE OR
PROBE
-[-"LENGTH (L) ATTENUATOR
I I!/
INPUT I
~c/
I '
E
MODEL 340 ij
I
Ill\ PROBE!
I '
If
I
I
1---- ER BELOW 30mV ·'l
,),
!j
·--ER ABOVE 30mV 1
I
20
1
I
I
I
I
I em
If
I I
10
f
~J
/V
,)
//
,
~
~
v v
,~~~ ...
~
...
::, b.:=
-~
...
.,.:::.;
0
20 30 50 70 100 200 300 500 700
FREQUENCY IN Me
ER _ I L•=1.2XI0-sf(cpslL(cm)
~ -COSL0- aS1Nl
0 a
::;;;; wC~o
Fig. 5. Model 340 Transmission Line Errors
Transmission line effects can be minimized by shorten-
ing the length of connection between source and Model
340. This may require the construction of specially
threaded adapters that will connect to the ground of
the Model 340 probe.
Transmission line effects may also be minimized
by
measuring in a matched 50 ohm transmission system.
For this application the Model 340 probe is first con-
nected to the Model 5340 Tee Adapter which is then
connected to the
50 ohm transmission line where the
measurement
is desired. The maximum vswr of this
. 5 •
system as a function of frequency is shown in figure 6.
This tabulation shows the maximum errors that can
exist due to reflections caused by the Model 340, assum-
ing the transmission line itself is perfectly matched.
1.30
1.20
0::
3=
en
>
1.10
1.00
/
L
/ v
f.--
~
v
,/
--
-v
100 200 300
FREQUENCY IN Me
Fig. 6. Model 5340 VSWR
INPUT >30mV
I
I
I
v
I INPUT
<37
/ v
500 700
2.5.9 Ground Current Errors can be particularly
troublesome whenever low-level, high frequency volt-
ages are measured. Special circuit precautions have
been made
in the Model 340 to reduce the effects of
ground currents -either currents of power line fre-
qunecy or high frequencies. However, particularly with
high frequency ground currents, it
is impossible to
completely eliminate these effects. Therefore every ef-
fort should be made to reduce the leakage from signal
sources into the power line ground. Avoid positioning
power line cords close to the Model 340 or to any low-
level sources that are being measured. Work at the
highest possible measurement levels.
2.5.10. Response and Waveform Errors are mini-
mized in the Model 340 because the instrument re-
sponds to the rms value of the input signal. This feature
is particularly important in the calibration of the Model
340. All high frequency calibration devices (Micro-
potentiometers, A-T Voltmeters, HF Transfer Volt-
meters) are rms-responding. When they are used to
calibrate a Model 340, errors due to distortion in the
signal sources will be minimized.
The rms feature of the Model 340
is likewise important
when measuring unknown voltages. Distortion
in the
voltage will not lead to the uncertain reading of a peak-
responding or average-responding instrument. How-
ever, particularly at high frequencies, response and
waveform errors must still be considered when using
the Model 340.
If the signal being measured is con-
nected to the Model 340 over a finite length of trans-
mission line -which in practice is always the case-
and if the signal contains higher frequency harmonics,
these harmonics will be transmitted over a longer elec-
trical length than the fundamental. This longer length
will alter the amplitude of the harmonics at the input
of the Model 340, in relationship to the amplitude of

the fundamental, and therefore alter the rms voltage as
measured by the Model 340. In addition, above 700 Me
the Model 340 itself no longer exhibits a flat response
but instead goes into a series resonant peak. Harmonics
above 700 Me will therefore be further emphasized and
the reading of the Model 340 will further depart from
a true rms indication of the signal voltage.
2.8 Overload Characteristics
The maximum ac voltage that should be applied directly to
the probe
is 10 volts. The maximum ac voltage that should
be applied to the probe attenuator
is 300 volts. Higher volt-
ages may damage one or both of the probe diodes.
TABLE I
DB LEVEL CONVERSION
Reference Level Subtract from
DB Readings on
FS Ranges
~--~~---·
f-
lmV
3mV
IV, I mW in 1000 Q (dbv)
70db 60db
f-----·-
--
-----~----
---
·-
0.775 V, I mW in 600 0 (dbm)
67.8 57.8
0.224 V, I mW in 50 Q 57.0 47.0
2.6 Use of the DB Scale
The db scale of the Model 340 is linear and reads from
0 to 10, corresponding to bottom scale and full scale voltage
readings.
To convert db readings to various reference levels,
use Table
I.
To simplify the conversion and to compute db levels of other
references, a handy db slide rule
is available from Ballantine
Laboratories on request, free of charge.
2.7 Effect of DC Component
The input signal to the probe is coupled to the two detector
diodes by 1000
pF capacitors. Any de component of the
input signal will be blocked by these capacitors and therefore
will not be measured.
The probe and probe attenuator have
been tested to withstand 300 V
de. Applying higher de
voltages may damage one or both of the probe diodes.
10mV
30mV
0.1 v 0.3 v 1.0 v 3.0V
50 db 40db
30db
20db 10db Odb
-- f--
--
f-----
1-----
47.8 37.8 27.8 17.8 7.8
-2.2
---
37.0 27.0 17.0 7.0
-3.0 -13.0
2.9 Effect of Power Line Voltage Variations
Operation is possible with line voltages of 105 to 125 volts.
Variation of the line voltage within this range will not affect
the sensitivity of the instrument by more than
1%. Some
readjustment of the
NULL may be necessary if measure-
ments are being made on either the 1 mV or 0.1 V ranges.
Transient variations in the line voltage may introduce addi-
tional noise on these two ranges as well.
2.10 DC Output
A de output is available at the rear of the instrument case
through a
BNC connector. The de output varies from 0.1
to 1.0 volts for each 10 db ac voltage range and is propor-
tional to the mean square of the ac input. The source im-
pedance is 20 kilohms.
3. CIRCUIT DESCRIPTION
The basic circuitry of this instrument is shown in figure 7,
Simplified Schematic, while a complete schematic and re- placement parts list are located at the end of this manual.
PROBE
CRI
CIA
R4
RFINPUT
R5
CIB
INPUT
AMP.
V I,V2
-czlJCIO
CHOPPER
Gl
Rl4
MID. SECTION OUTPUT AMP,
ATTEN. V3 ,V4
R56flSCALE
R61
R58
-= I'
METER
L---------------,
+
C3
R6
NULL
fRI04l
+
SYM.
ADJ.
RBI
Fig. 7. Model 340 Simplified Schematic
- 6 -
R59
ft
DC
-=LIN.
Ql
+
DC
OUT.
R62
R60
DC OUTPUT

3.1 Probe
The probe of the Model 340 is designed to convert ac volt-
ages, 300 fL V to 3 V, to equivalent de voltages on an rms
basis over a frequency range from 100
kc to 700 Me.
The probe consists, electrically, of a single input-dual output
ceramic input capacitor, C1, of 1000- 1000 pF. The input
ac signal voltage is coupled through this capacitor to the
two germanium diode detectors, CR1 and CR2, which are
connected, in opposite polarity, to ground through R4 and
RS. These resistors serve to improve the high frequency
response
by introducing a correction to the series resonance
of the diodes.
B~th diodes are always operated with less than 30 mV ap-
phed ac voltage. They are therefore always operated in that
region where their characteristics can be described
as square-
law. The diodes are specially selected for resistance, thermal
chara~teristics, and frequency response. The de outputs from
the dwdes, one negative and one positive, are connected over
decoupling filters R1-C2 and R2-C3 to a special low-noise
cable and then to the Model 340 chassis input. After being
converted to a 94 cps signal by means of a chopper, ampli-
fied,_ and detected, an equivalent de signal is averaged and
has lts square-root taken in the indicating meter to produce
a reading proportional to the rms of the ac input voltage
to the probe.
R6 is use? to inject a current into RS controlled by the
NUL~ adjustment. The resulting voltage drop, adjusted in
magmtude and polarity, serves to balance out any residual
de output from the probe with no
ac signal input. R3 is
connecte~ to RS to maintain electrical symmetry at high
frequenoes.
The pro?e is ~oused in a double-walled tube to provide
thermal msulanon to the diode circuits. The inner wall car-
ries the signal ground. It is connected at one end to the
diode grounds and the ground braids of the probe cable,
and at the other end
is terminated in a Ys-24 thread to
match the probe adapters.
3.1. ~ Model 1340 Probe Attenuator is designed to
prov1de a stable 40 db attenuation over a frequency
range of 100 kc to 700 Me when connected ahead of
a Model 340 probe. This attenuation is used to reduce
ac
input signals from 30m V to 3 V to the range 300 p. V
to_ 30 mV where they can be measured by the probe
w1th an rms response. Failure to use such an attenuator
ahead
of the probe would drive the probe diodes out
of their square-law region and the resulting response
would no longer be rms.
The attenuation is provided by a specially constructed,
factory-adjusted capacitor
Cl and a fixed, mica disc
capacitor, C2. Physically the Model 1340 Probe At-
tenuator screws directly on to the Ys-24 thread of the
probe. Its
input is constructed exactly as the probe
input -flexible bellows center conductor and Ys-24
ground shell. All adapters for the probe connect as
well to the probe attenuator.
3.1.2 Model 2340 Coaxial Adapter is used to con-
vert the probe or probe attenuator input to a coaxial
connector mating with Type N or Type
BNC female
connectors.
It adds approximately 0.3 inch of trans-
mission line between the probe input and the front face
of a mating Type N connector and about 1 pF of added
input capacitance.
- 7 -
3. 1.3 Model 4340 Probe Tip is designed for in-circuit
measurement below approximately 100
Me. It consists
of a stainless-steel tip, covered with a spring-loaded
nylon insulator, that can be made either to press against
the point of measurement or be hooked on to a circuit
":ire. An a_ttached ground cable with alligator clip pro-
vldes the s1gnal ground.connection. The inductance of
this ground lead, together with the added length of
transmission path of the probe tip, limits the use of
this adapter to relatively low frequencies.
3.1.4 Model 5340 Tee Adapter is designed to allow
the use
of the Model 340 for voltage measurements on
matched 50
ohm transmission lines. It consists of a
milled aluminum block with a Type N male
input con-
nector and Type N female output connector that can
be inserted in the transmission line under measurement.
The Model 340 probe, with or without probe attenu-
~tor, depending on the voltage being measured, screws
lnto the threaded portion of the aluminum block and
makes connection with the center conductor of the
block.
On the opposite side of the block is an insulated
knob that
is adj1.1sted to one of two positions -for
input signals above or below 30 mV. This knob con-
trols_ a pair of vanes that compensate for the change in
loadmg of the Tee Adapter when either the Model 340
with or without its probe attenuator is used.
Figure 6 shows the maximum uncertainty in measured
voltage that is introduced by the vswr of the Model
5340 Tee Adapter.
3.1.5 Model 6340 High Voltage Attenuator adapts
the Model 340 to voltage measurements from 3
to
300 V over the frequency range of 0.1 to 100 Me.
It is connected to the Model 1340 Probe Attenuator
":hich in turr: !s connected to the probe itself, and pro~
v1des an addmonal 40 db of voltage attenuation. The
added error is 1% from 0.1 to 10 Me and 2% from
10 to 100 Me.
3.2 Chopper Input
To convert the de output of the probe to ac, this instrument
uses a mechanical modulator or chopper, which
is regarded
as the best choice for this purpose, particularly because of
the low level involved.
Of the various conversion means
available the mechanical modulator displays:
a. The highest conversion efficiency
b. The lowest residual noise level
c. The lowest residual de
d. The lowest de drift
To avoid dependence on power supply frequency and to re-
duce the effects of power supply hum, the chopper operates
at a frequency of 94 cps.
The signal frequency after con-
version i~ therefore ?~ cps. The chopper is driven by a
94 cps, blStable mulnv1brator using two rugged transistors
which convert
12 volts de to square wave ac. Since the tran-
sistors operate only as switches, they dissipate very little
power, leading to low internal temperatures and long life.
RS? permits a small adjustment of operation frequency,
whlle R81 provides for an adjustment of symmetry. It should
be noted that
if the drive supply (7 pin connector on top
of
unit) is removed with the power on, and then recon-
nected, the transistors will be saturated and the unit will not
restart until the .power
is interrupted and reapplied. There
will be no damage done.

The input chopper is of the single pole, double throw type
using gold alloy, twin contacts, designed especially for low
level operation. The de signals are coupled to the chopper
by low-pass filters formed by C5, R10-C8 and C6, Rll-C9.
ClO, C11, R12, and R14 couple the resulting ac output from
the chopper, at the correct impedance level, to the input
amplifier.
3.3 Input Amplifier
The ac signal·(94 cps) from the chopper is sent to an input
amplifier having a gain of approximately 1,000. The ampli-
fier uses a dual triode, V1, and a pentode, V2, with overall
feedback stabilization
of 26 db or greater. To reduce noise
the bandwidth
is severely restricted by making the plate load
of the last stage a parallel resonant circuit tuned to the signal
frequency.
To further reduce noise the input triodes are
operated semi-starved, and metal film and deposited carbon
type resistors are used at all critical points. The heaters
of
the input triode are operated on de (rectified and filtered ac)
while the plate and screen supply for all these tubes are
stabilized by a gaseous regulator tube.
3.4 Midsection Attenuator
Signals from an input amplifier are sent to the output ampli-
fier via the midsection attenuator. This attenuator,
in addi-
tion to providing range switching, permits the input signal-
to-noise ratio to increase whenever it introduces attenuation.
The attenuator
is a simple resistive-divider type and employs
deposited carbon resistors.
3.5 Output Amplifier and Signal Recrifier
Signals from the midsection attenuator are further amplified
in the output amplifier, which in configuration is very similar
to the
input amplifier. A dual triode, V3, and a pentode, V4,
are operated with overall feedback stabilization
of 26 db.
Again in the interest
of low noise the triodes are operated
semi-starved, while the plate and screen potentials are de-
rived from a gaseous regulator tube.
In contrast to the input amplifier, where all three tubes are
operated to provide voltage gain, the output tube of this
amplifier serves to convert voltage to current. This output
current drives two rectifiers, CR5 and CR6. CR5 delivers
a half-wave rectified current to the indicating meter Ml.
CR6 delivers a similar current, of opposite polarity, to load
resistors R62 and R60 and the resulting voltage drop,
fil-
tered, is available as a de output proportional to the mean
square
of the ac input to the probe. The currents through
both rectifiers are combined and go either to signal ground
directly or through compensating resistors R75, R76, R77
and R78 to ground. Compensation
is necessary on the 1 mV
and 0.1 V ranges for the residual noise of the probe and
amplifier, and on the 30 mV and 3 V ranges for a slight non-
linearity in probe diode square-law characteristic.
3.6 Power Supply
All necessary operating potentials are derived from a line
operated power supply.
High potentials for plates and
screens are obtained from rectified
ac, rc filtered, and gaseous-
tube stabilized. All tube heaters except
Vl are operated
on ac balanced with respect to ground. The heater of V1
is operated on rectified ac with rc filtering. R92, a potenti-
ometer across this de supply,
is adjusted to provide mini-
mum hum
in the input stages.
4. MAINTENANCE
4.1 General
The Model 340 is designed for extended trouble-free service.
High grade components operated below rating and low
operating temperature result
in more than 3,000 hours of
expected operating periods without the need for amplifier
tube changes or circuit adjustments.
The purpose of periodic maintenance procedures
is to assure
the specified accuracy, check the condition
of the voltmeter
and detect and replace deteriorated tubes or components
before they have an appreciable effect on instrument per-
formance. The procedure
is designed not only to measure
and correct voltmeter performance
at the time of test, but
to foresee the possible troubles and guarantee the instrument
accuracy through the next maintenance period.
4.2 Recommended Maintenance consists of two types of
periodic checks.
4.2.1 2,000 hour checks.
4.2.2 4,000 hour checks.
4.3 Necessary Maintenance Equipment
4,3.1 Stable Signal Source, adjustable from 10 mV
to 1 V, capable
of being set to ± ~ %, frequency in
range 100
kc- 1 Me.
- 8 -
4.3.2 Sensitive AC Vacuum Tube Voltmeter, such
as Ballantine Model 300H.
4.3.3 Sensitive DC Vacuum Tube Voltmeter, such
as Ballantine Model 365.
4.3.4 Tube Checker
4.4 Removal of the Case
Place the voltmeter face down on a table. Remove the power
cord and the two
#10 binder head screws at the rear of the
case. Lift
up the case. To replace the case, proceed in re-
verse order.
WARNING: When the instrument is operated without
the case the danger of electric shock exists. Take ex-
treme care
not to come in contact with high voltage points.
The highest voltage
on the chassis is 400 V de.
4.5 2,000 Hour Check consists of the following:
4.5.1 Scale Adjustment checks the scale linearity of
the logarithmic indicator.
It is equivalent to the zero
adjustment of a linear meter. For such adjustment
Set
Function Switch
. Range Selector
To
METER
10 mV

Apply a stable source of 100 kc- 1 Me to the probe
input. Adjust the amplitude to produce a meter reading
of exactly
10 on the upper voltage scale. Reduce the
source by exactly 10 db. The meter should now indicate
exactly 1
on the lower voltage scale. If it does not,
rotate the SCALE ADJ control, R61, located at the
right side of the front panel. Repeat this procedure
until readings of exactly 10 and 1 are obtained.
4.5.2 Sensitivity Adjustment corrects for any change
in overall gain due
to aging of amplifier components,
tubes, probe diodes, or probe attenuator. For sensitivity
adjustment:
Set
Function Switch
Range Selector
To
NULL
1
mV
Adjust NULL adjustment according to paragraph
2.4.1.1. Then:
Set
Function Switch
Range Selector
To
METER
10 mV
Apply 10 mV, ±Y-4%, from a stable source of 100 kc-
1 Me to the probe input. The meter should read exactly
10 mV. If not, adjust SENS control located at the right
side of the front panel. Then:
Set
Function Switch
Range Selector
To
METER
1 v
Attach the Probe Attenuator, Model 1340, to the probe.
Apply 1
V, ± Y-4%, from a stable source of 100 kc -
1 Me to the probe attenuator.
The meter should read
exactly 1 V. Ordinarily no adjustment to the probe
attenuator should be necessary.
If the error on the 1 V
range is less than 1 Yz%, the SENS control should be
readjusted to split this error with and without probe
attenuator.
If the error on the 1 V range is greater than
1Yz%, C1 should be adjusted for a 1 V reading by
rotating the
input insulator of the probe attenuator-
whose threads have been sealed with Loctite- with a
wrench designed to fit the two .062 inch holes spaced
.280 apart. After adjustment, the insulator should be
resealed with Loctite.
4.5.3 Noise Check is necessary to insure that the
original low noise level of the instrument
is not in-
creased by aging of components or environmental con-
ditions.
At Ballantine Laboratories the noise is mea-
sured
as follows: With probe open-circuited and
shielded,
Set
Function Switch
Range Selector
To
NULL
1 mV
- 9 -
Adjust NULL control for minimum indication. Record
the
db scale meter reading. Then:
Set
Function Switch
Range Selector
To
NULL
30 mV
Record db scale meter reading.
The difference in the
two meter readings should
not exceed 1 db. If the
difference i~ meter readings does exceed this figure, all
components in the probe and input circuitry up to and
including
V1 may be suspected.
The noise level is of greatest importance when making
measurements on either the 1 mV or
0.1 V range. On
other ranges the noise level can be appreciably higher
and
not affect the accuracy of measurement.
4.5.4 Range Switching Check determines the accu-
racy
of the midsection attenuator that is connected be-
tween V2 and V3. To check this attenuator, make the
NULL adjustment per paragraph 2.4.1.1 and then:
Set
Function Switch
Range Selector
To
METER
30 mV
Apply a stable source to the probe input of approxi·
mately 15 m V. Adjust the amplitude of the source until
the meter reads exactly
1.5 on the lower voltage scale.
Then reduce the source by precise steps of 10 db, turn-
ing the range selector progressively to 10, 3 and 1 m
V.
The meter should continue to indicate 1.5 ±0.02 on
the lower voltage scale.
4.5.5 DC Output Check determines the accuracy of
the de output.
Set
Function Switch
Range Selector
To
METER
10 mV
Apply a stable source from 100 kc- 1 Me to the probe
input and adjust until the meter reads exactly 10 mV.
Now connect an accurate de indicator to the de output
BNC connector at the rear of the instrument. This de
indicator should have high enough resistance
not to
load the 20
kQ de source resistance. The de indication
should be 1.0 V ±
1%. If it is not, adjust R60, the
DC Output Adjustment (see figure 8).
Now reduce the amplitude of the ac source by exactly
10 db to 3.17 m V. The de indication should be 0.1 V
± 1%. If it is not, adjust R63, the DC Linearity
Adjustment (see figure
8) .
4.5.6 Stability with Line Voltage checks the overall
condition of the instrument.
Set
Function Switch
Range Selector
To
METER
10 mV

Apply a stable source of 100 kc - 1 Me to the probe
input. Adjust the amplitude of the source to obtain a
meter reading of exactly 10 m
V. Check the line voltage
to make sure it
is 115-117 volts. Now adjust the line
voltage to 105 volts, and then to 125 volts.
The meter
indication should not change by more than
1%. If it
does, the chopper supply voltage or frequency may be
in error, or the amplifier tubes may have aged beyond
acceptable limits (see 4.6.1 and 5.3).
4.6 4,000 Hour Check consists of all the tests listed under
the 2,000 hour check.
In addition, all tubes should bechecked
and the chopper supply adjusted.
4.6.1 Chopper Supply Adjustment checks the fre-
quency and symmetry of the chopper supply.
Set To
Function Switch METER
Range Selector
10 mV
Apply a stable
10 mV signal, 100 kc - 1 Me, to the
probe input. Adjust R82, Frequency Adjustment, for
a maximum meter indication (see figure
8) .
Connect a wideband
ac voltmeter across terminals 36
and 38 on the chopper driver board. Adjust R81,
Symmetry Adjustment, for a maximum voltmeter read-
.ing. Readjust R82, if necessary, for a maximum Model
340 meter indication (see figure 9) .
5. SERVICING AND TROUBLESHOOTING
In case of voltmeter malfunction, servicing by the user
is feasible provided skilled personnel and recommended
equipment are available, and ·the procedure outlined in this
and Section 4 are followed.
It should be mentioned that the
procedures
in this manual are of a simplified nature. Refined
and comprehensive service and calibration require special-
ized equipment not normally available to the average user.
Therefore
if trouble develops which cannot be corrected by
the procedures outlined here, or when a most accurate cali-
bration is desired, it is recommended that the instrument be
returned to Ballantine Laboratories, Inc.
The instrument
should
in all cases be preceded by a letter stating the nature
of the trouble or the desired service. (
See Section 6 for
shipping instructions.)
5.1 Necessary Equipment
5.1.1 Stable Signal Source, adjustable from 10 mV
to 1 V, capable of being set to
±~%.frequency in
range 100
kc- 1 Me.
5.1.2 Sensitive AC Vacuum Tube Voltmeter, such
as Ballantine Model 300H.
5.1.3 Sensitive DC Vacuum Tube Voltmeter, such
as Ballantine Model 365.
5. 1.4 Tube Checker
5.2 Simple Service Problems
5.2.1 Removal
of the Instrument Case is required
for all servicing.
Place the voltmeter face down
on a table. Remove the
power cord and the two #10 binder head screws at
the rear of the
case. Lift up the case. To replace, pro-
ceed in the reverse order.
WARNING: When instrument is operated without
the case, the
danger of electric shock exists. Take
extreme care not to come in contact with the high
voltage points.
The highest voltage on the chassis is 400 V de.
5.2.2 Pilot Light Replacement
The pilot lamp, Type 1815, is accessible by unscrewing
the red plastic cap located on the front panel.
5.2.3 Fuse Replacement
The use is of the Slo-Blo type and is rated at 0.4 A for
115 V operation and 0.2 A for 230 V operation. The
fuse holder
is of the extractor post type and is located
on the front panel.
5.2.4 Line Voltage Conversion
It is possible to operate the Model 340 for either a
115 V or 230 V line supply. The line voltage for which
the instrument is connected
on leaving the factory is
indicated on a decal located adjacent to the line cord.
At the rear of the instrument on the power cord re-
ceptacle bracket are three terminals marked 1, 2, and 3.
The power transformer connections are as follows:
Terminal Power Transformer Leads
115 v
230 v
1 Black, Black-Red Black
2
No Connection Black-Yellow,
Black-Red
3 Black-Yellow, Black-Green Black-Green
5.3 General Instructions
When there is malfunction that is not simply corrected by
any of the normal calibration adjustments (see Section 4)
the following procedure is recommended:
-10 -
5.3.1 Check all tubes on a reliable tube tester; replace
any tubes which exhibitlow gm, shorts, grid current, etc.
5.3.2 If tube replacement does not restore normal
operation, check all de and
ac operating potentials and
compare with those listed
on schematic (Fig. 10)
located at the rear of the manual. An abnormal voltage
may give a clue to the nature of the
def~;ct.

5.3.3 If neither 5.3.1 nor 5.3.2 indicates the nature of
the difficulty, make a thorough physical examination
for broken or discolored components, broken leads,
defective connections, etc.
5.4 Signal Tracing
If the simple checks outlined in section 5.3 fail to reveal the
cause of malfunction, signal tracing should be tried
Set To
Function Switch METER
Range Selector 10 mV
Apply a stable source of 10 m V, 100 kc- 1 Me, to the input
of the probe.
With a sensitive, accurate, high impedance ac
voltmeter, check the ac signal voltages and compare with
those shown on the schematic (Figure 10) located at the
end of this manual. Any radical difference from those indi-
cated may provide a clue to the difficulty.
5.5 Chopper Replacement
If it has been determined that the chopper needs replace-
ment, the procedure
is as follows (see figures 8 and 9) :
5.5.1 Remove the instrument case.
5.5.2 Remove the three screws that hold the shield
covering the input circuitry.
5.5.3 Disconnect the three bare copper leads running
from the base
of the chopper. Note the connection for
each lead before removing.
5.5.4 Remove the 7 pin top connector from the top
of the chopper.
5.5.5 Remove the 2 screws which secure the chopper
base to the chassis.
5.5.6 The chopper may now be removed from the
instrument.
5.7 Troubleshooting Chart
5.5.7 Install the new chopper, observing the reverse
of the procedure above. Use the special
16w thermal
emf solder provided.
5.6 Probe Replacement
The two signal diodes in the probe may be damaged by
applying excessive
ac or de voltages to the probe. Should
the diodes be damaged the sensitivity of the instrument will
be greatly
in error and cannot be corrected by the panel
SENS control.
It
is recommended that if the probe diodes, or any other
probe components, are damaged, the entire instrument be
returned to Ballantine Laboratories for repair and recalibra-
tion. Special equipment and experienced personnel are avail-
able for this work.
Probe repairs by the user are most easily accomplished by
replacing the entire probe. The following procedure should
be followed:
5.6.1 Obtain a replacement probe assembly from
Ballantine Laboratories. Specify the serial number of
the instrument.
5.6.2 Remove the instrument case (see 5.2.1).
5.6.3 There are four probe connections just behind
the front panel, three connected to the feed-thru
capacitors and one to a ground lug. Carefully unsolder
these four connections, then unclamp the two coaxial
cables. The probe cable can now be pulled through
the opening in the front panel.
5.6.4 Insert the new probe cable through the panel,
reclamp the coaxial cables, and solder the four connec-
tions
as before. Use the special low emf solder pro-
vided. Use
as little solder as possible.
5.6.5 Check the sensitivity of the instrument, and ad-
just if necessary, following the procedure of paragraph
4.5.2.
To assist in troubleshooting, this chart lists symproms, possible causes, and where possible, perti-
nent sections of this manual.
Symptoms Possible Cause Pertinent
and/or Remedy Sections
Instrument inoperative
No power, fuse blown
5.2.3
Pilot light does not light Defective power supply
3.6
Instrument indication with Function switch
in NULL position
2.5.3
no input
NULL control improperly adjusted
2.3
Noisy input tube V1
4.5.3
Defective chopper
5.5
Instrument apparently operating Function switch in STANDBY
2.5.1
but no indication Defective chopper
5.5
- 11 -

Symptoms Possible Cause Pertinent
and/ or Remedy Sections
Instrument is out of calibration: Function switch in NULL 2.5.3
a.
on all ranges at low R61 SCALE adj
off 4.5.1
frequencies R56 SENS adj off 4.5.2
Defective tube or component
Defective probe 2.7, 2.8, 5.6
b.
on all ranges above 30 mV Model 1340 attenuator
off 4.5.2
at low frequencies
c. on 1 mV and 0.1 V ranges R104 NULL
ad j off 2.4.1.1
R57, R71, R72, R75, R76
3.5
d. on 30 mV and 3 V ranges R73, R74, R77, R78 3.5
R31- R34 3.4
e.
on 3 mV and 0.3 V ranges R31-R34
3.4
f.
on 10 mV and 1 V ranges
R31- R34 3.4
g.
on all ranges at high Defective probe 3.1, 5.6
frequencies
h.
on all ranges above 30 mV Defective Model 1340 Probe Attenuator 3.1.1
at high frequencies
Excessive drift on most Instrument
in warm or drafty location
sensitive range Defective
input component
Excessive change
in indication Weak or defective tubes
with line voltage change Chopper supply improperly adjusted 4.6.2
Chopper drive voltage low
Indication normal, de output C30, C31 defective or shorted
3.5
low or absent Defective resistor R59, R60, R62, R63
3.5
Defective diode CR6
Chopper supply frequency Defective resistor
R81- R85 3.2
incorrect, not possible to Defective capacitor, C35, C36
3.2
correct with R82 Defective chopper
Cl
5.5
Defective transistor Q1, Q2 3.2
- 12 -

6. SHIPPING INSTRUCTIONS
If it should be necessary to return the instrument to Ballan-
tine Laboratories, Inc. make certain that at least four inches
of padding material surrounds the instrument to prevent
damage during shipment. Ship via Railway Express or
motor truck to
BALLANTINE LABORATORIES, INC.
90 Fanny Road
Boonton,
New Jersey
- 13-

V7
OB2WA
V6
OA2
V5
6X4
Fig. 8. Model 340- Right Hand Side View
. 14 -

LINE VOLTAGE
CONVERSION
Figure 9. Model 340- Left Hand Side View
Input Shield Removed
- 15 -
-----Ql
-----Q2
R81
SYM. ADJ.